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            <h2 class="title" style="clear: both"><a id="rep_ex_chan"></a>Ex_rep_chan: a Replication Manager channel example</h2>
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      <p>
        Ex_rep_chan, found in the
        <code class="filename">examples/c/ex_rep_chan</code> subdirectory
        of the Berkeley DB distribution, is a simple but complete
        demonstration of a replicated application that uses the
        Replication Manager feature of channels to perform write
        forwarding. The application is a mock stock ticker. Although
        similar to the ex_rep_mgr example program, this example
        differs in that it provides an example of using Replication
        Manager message channels. Any site accepts a command to write
        data to the database. If the site is a client, then, using the
        channels feature, the application forwards the request to the
        master site. If the site is a master then the request is
        automatically handled locally. You can read and write stock
        values at any site without needing to know what site is
        currently the master. 
    </p>
      <p>
        The set of supported commands can be viewed with either the
        <span class="bold"><strong>help</strong></span> or the <span class="bold"><strong>?</strong></span> command. Several commands work
        with key/data pairs where the key is a stock symbol and the
        data is its value.
    </p>
      <p>
        The command to retrieve and print the current site's
        database contents is <span class="bold"><strong>print</strong></span> or
        simply an empty input line. To read the contents of the
        master's database from any site use the <span class="bold"><strong>get key key ...</strong></span> 
        command. That command will
        forward the read request to the master if necessary and return
        the key/data pairs for all given keys. 
    </p>
      <p> 
        There are two commands to put data into the database. Both
        commands take one or more key/data pairs, all of which are
        written into the database in a single transaction at the
        master site. The <span class="bold"><strong>put</strong></span> command
        sends the data to the master site, and simply waits for a
        status response. The <span class="bold"><strong>put_sync</strong></span>
        command sends the data to the master site, and uses a
        transaction token returned by the master to wait for the
        contents of that put to be available on the local site. This
        serves as a demonstration of the <a class="link" href="rep_ryw.html" title="Read your writes consistency">read
        your writes</a> consistency feature. 
    </p>
      <p> 
        The Makefile created by the standard UNIX configuration
        will build the ex_rep_chan example on most platforms. Enter
        "make ex_rep_chan" to build it. 
    </p>
      <p>
        The synopsis for the program is as follows: 
    </p>
      <p>
        <code class="literal">ex_rep_chan <span class="bold"><strong>-h home</strong></span>
        <span class="bold"><strong>-l host:port</strong></span> [<span class="bold"><strong>-MC</strong></span>] [<span class="bold"><strong>-r
        host:port</strong></span>] [<span class="bold"><strong>-R
        host:port</strong></span>] [<span class="bold"><strong>-p
        priority</strong></span>] [<span class="bold"><strong>-v</strong></span>]</code>
    </p>
      <p>
        The options are as follows: 
    </p>
      <div class="variablelist">
        <dl>
          <dt>
            <span class="term">
                <span class="bold"><strong>-h</strong></span>
            </span>
          </dt>
          <dd>
                Specify a home directory for the database
                environment.
            </dd>
          <dt>
            <span class="term">
                <span class="bold"><strong>-l</strong></span>
            </span>
          </dt>
          <dd>
                Listen on local host "host" at port "port" for
                incoming connections.
            </dd>
          <dt>
            <span class="term">
                <span class="bold"><strong>-M</strong></span>
            </span>
          </dt>
          <dd>
                Configure this process as a master.
            </dd>
          <dt>
            <span class="term">
                <span class="bold"><strong>-C</strong></span>
            </span>
          </dt>
          <dd>
                Configure this process as a client.
            </dd>
          <dt>
            <span class="term">
                <span class="bold"><strong>-r</strong></span>
            </span>
          </dt>
          <dd>
                Identifies the helper site used for joining the
                group. 
            </dd>
          <dt>
            <span class="term">
                <span class="bold"><strong>-R</strong></span>
            </span>
          </dt>
          <dd> 
                Identifies a remote peer to be used for joining
                the group. This peer is used for syncing purposes. See
                <a class="xref" href="rep_mastersync.html#rep_c2c_sync" title="Client-to-client synchronization">Client-to-client synchronization</a> for more
                information. 
            </dd>
          <dt>
            <span class="term">
                <span class="bold"><strong>-p</strong></span>
            </span>
          </dt>
          <dd> 
                Set the election priority. See <a class="xref" href="rep_elect.html" title="Elections">Elections</a>
                for more information.
            </dd>
          <dt>
            <span class="term">
                <span class="bold"><strong>-v</strong></span>
            </span>
          </dt>
          <dd>
                Indicates that additional informational and
                debugging output should be enabled.
            </dd>
        </dl>
      </div>
      <p> 
        A typical ex_rep_chan session begins with a command such as
        the following, to start a master:
    </p>
      <pre class="programlisting">ex_rep_chan -M -h DIR1 -l localhost:30100</pre>
      <p>
        and several clients: 
    </p>
      <pre class="programlisting">ex_rep_chan -C -h DIR2 -l localhost:30101 -r localhost:30100
ex_rep_chan -C -h DIR3 -l localhost:30102 -r localhost:30100
ex_rep_chan -C -h DIR4 -l localhost:30103 -r localhost:30100</pre>
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